African dust particles over the western Caribbean - Part I: Impact on air quality over the Yucatán Peninsula

On a global scale, African dust is known to be one of the major sources of mineral dust particles, as these particles can be efficiently transported to different parts of the planet. Several studies have suggested that the Yucatán Peninsula could be influenced by such particles, especially in July, associated with the strengthening of the Caribbean low-level jet. Although these particles have the potential to significantly impact the local air quality, as shown elsewhere (especially with respect to particulate matter, PM), the arrival and impact of African dust in Mexican territory has not been quantitatively reported to date. Two short-term field campaigns were conducted to confirm the arrival of African dust on the Yucatán Peninsula in July 2017 and July 2018 at the Mérida atmospheric observatory (20.98° N, 89.64° W). Aerosol particles were monitored at ground level using different online and off-line sensors. Several PM_2.5and PM10 peaks were observed during both sampling periods, with a relative increase in the PM levels ranging between 200% and 500% with respect to the normal background conditions. Given that these peaks were found to be highly correlated with supermicron particles and chemical elements typically found in mineral dust particles, such as Al, Fe, Si, and K, they are linked with African dust. This conclusion is supported by combining back trajectories with vertical profiles from radiosondes, reanalysis, and satellite images to show that the origin of the air masses arriving at Mérida was the Saharan Air Layer (SAL). The good agreement found between the measured PM₁₀concentrations and the estimated dust mixing ratio content from MERRA-2 (Version 2 of the Modern-Era Retrospective analysis for Research and Applications) corroborates the conclusion that the degradation of the local (and likely regional) air quality in Mérida is a result of the arrival of African dust.